Ovens



'D- E. EASON Oct. 5, 1965 OVENS Filed Jan. 30, 1963 United States Patent Greenford, Middlesex, & Company Limited,

This invention relates to ovens of the kind in which heating is effected by micro-wave energy.

The invention has for its object to provide an oven having a door structure which closes the cavity and as far as possible, prevents the external radiation of energy.

Features and advantages of the invention will be apparent from the following description of one embodiment thereof, given by way of example, with reference to the accompanying drawings, in which,

FIGURE 1 shows a diagrammatic sectional side view of an oven constructed in accordance with the invention, and

FIGURE 2 is an enlarged sectional detail of the oven shown in FIGURE 1.

In the micro-wave oven shown in FIGURE 1 an oven cavity 5 formed by walls 6 is closed by a door structure 7. Micro-wave power is propagated into the cavity 5 by means not shown. Said means may be of the type described in the specification of a co-pending patent application Serial No. 254,925 filed on January 30, 1963 in the name of Peter Harold Smith.

To attenuate the radiation of the micro-wave power escaping around the door structure, the edges of the cavity walls and the door structure are provided with quarter-wavelength chokes formed by respective flanges 8 and 9. The flanges 8 and 9 lie substantially parallel and in contact when the door is closed.

However, the flanges 8 and 9 become distorted due to the heat of the oven and if they alone were provided gaps would appear between these flanges thus reducing the effective attenuation.

Safety makes it necessary to limit the radiation level from these ovens to below 10 milliwatts per square centimetre.

In addition to the flanges therefore a thin, flexible metal plate 10 is provided which is spring mounted on the door structure 7.

When the door is closed the plate 10 is forced against the flange 8 by its spring mounting and owing to its flexibility the plate takes up the contour of the flange thus forming a good seal for the oven cavity irrespective of any misalignment of the door structure and oven.

In this way the micro-wave power cannot escape between the plate 10 and the flange 8 and any power that passes through the plate is attenuated by the quarterwavelength choke formed by the flanges 8 and 9 before it passes out to the surroundings.

The plate 10 has the same area as the door 7 and is formed of stainless steel.

The plate 10 is spring mounted on the door structure 7 by means of a series of mountings provided around the flange 9 and these mountings are sufliciently close together to cause the plate 10 to take up the contour of the flange 8 when the door is closed.

One of the mountings is shown enlarged in FIGURE 2. The mounting comprises a rod 12 attached to the ice plate 10 by a countersunk head screw 13. The rod 12 projects through an aperture 14 in the door flange 9, and a split pin 15 passes through a hole in the rod 12. A spring 16 is held compressed between the split pin 15 and a door cover 17 which is attached to the door structure 7.

The mounting allows the plate 10 to be moved between the position shown in FIGURE 2 and a position abutting the door flange 9.

In a particular construction of the micro-wave oven the cavity was approximately 14 inches cube.

The frequency used corresponded to a wavelength of 12 centimetres and the dimension D (see FIGURE 2) of the flanges 8 and 9 was about 3 centimetres i.e. one quarter wavelength. The plate 10 was made from 28 S.W.G. stainless steel and with the door open the plate stood proud of the door flange 9 by /8 inch. The mountings were spaced apart at a pitch of 1 /2 inches around the edge of the door.

In this oven the power propagated into the cavity was about 2 kilowatts.

I claim:

1. A radio frequency oven comprising a box-like structure for holding food to be heated and having an access opening in one wall thereof, flange means attached to said structure so as to surround said opening, a door frame, a thin flexible plate arranged to close said opening by its annular contact with said flange means, a plurality of spring attachments resiliently mounting said plate on said frame to form door means, each of said spring attachments comprising a rod attached at one end to said plate and projecting through a respective hole in said frame, abutment means attached to the projecting portion of said rod, and a coil spring compressed between said door frame and said abutment means, said spring attachments being attached to said plate at intervals around its annular contact area, whereby said plate is urged into said radio frequency tight contact with said flange means when said door means is in its closed position.

2. A radio frequency oven comprising a box-like structure for holding food to be heated and having an access opening in one wall thereof, flange means attached to said structure so as to surround said opening, a door frame, a thin flexible plate arranged to close said opening by its annular contact with said flange means, said plate being dimensioned so that the area of said annular contact is M4 wide, a plurality of spring attachments resiliently mounting said plate on said frame to form door means, said spring attachments being attached to said plate at intervals around its annular contact area, whereby said plate is urged into radio frequency tight contact with said flange means when said door means is in closed position.

3. A radio frequency oven comprising a box-like structure for holding food to be heated and having an access opening in one wall thereof, said structure being defined by a conductive shell, flange means integral with a por tion of said shell and surrounding said opening, a door frame, a thin flexible plate arranged to close said opening by its annular contact with said flange means, and a plurality of spring attachments interconnected between said plate and said door frame at intervals around its annular contact area for resiliently supporting said plate to urge said plate into radio frequency tight contact with said flange means when said door means is in its closed position, each of said spring attachments comprising a References Cited by the Examiner rod attached at one end to said plate and projecting through a respective hole in said door frame, abutment UNITED STATES PATENTS means attached to the projecting portion of said ro 2,500,676 3/50 Hall et a1 219-1055 and a coil spring compressed between said door fram 5 2,778,911 1/57 Valentine 219-1055 and said abutment means, thereby to urge said p e 2,958,754 11/60 Hahn 219-10.55 away from said frame for radio frequency tight contact against said flange means. FOREIGN PATENTS 4. An oven as set forth in claim 3, wherein said plate 1,262,776 5/60 Fran e,

is dimensioned so that the area of said annular Contact is M4 wide. RICHARD M. WOOD, Primary Examiner. 

1. A RADIO FREQUENCY OVEN COMPRISING A BOX-LIKE STRUCTURE FOR HOLDING FOOD TO BE HEATED AND HAVING AN ACCESS OPENING IN ONE WALL THEREOF, FLANGE MEANS ATTACHED TO SAID STRUCTURE SO AS TO SURROUND SAID OPENING, A DOOR FRAME, A THIN FLEXIBLE PLATE ARRANGED TO CLOSE SAID OPENING BY ITS ANNULAR CONTACT WITH SAID FLANGE MEANS, A PLURALITY OF SPRING ATTACHMENTS RESILIENT MOUNTING SAID PLATE ON SAID FRAME TO FORM DOOR MEANS, EACH OF SAID SPRING ATTACHMENTS COMPRISING A ROD ATTACHED AT ONE END TO SAID PLATE AND PROJECTING THROUGH A RESPECTIVE HOLE IN SAID FRAME, ABUTTMENT MEANS ATTACHED TO THE PROJECTING PORTION OF SAID ROD, AND A COIL SPRING COMPRESSED BETWEEN SAID DOOR FRAME AND SAID ABUTMENT MEANS, SAID SPRING ATTACHMENTS BEING ATTACHED TO SAID PLATE AT INTERVALS AROUND ITS ANNULAR CONTACT AREA, WHEREBY SAID PLAT IS URGED INTO SAID RADIO FREQUENCY TIGHT CONTACT WITH SAID FLANGE MEANS WHEN SAID DOOR MEANS IS IN ITS CLOSED POSITION. 